Some exceptions to the rule

BMI does not differentiate between body fat and muscle mass. This means there are some exceptions to the BMI guidelines :
   

Muscles – body builders and people who have a lot of muscle bulk will have a high BMI, but are not overweight...

Physical    disabilities – people who have a physical disability and are unable to walk may have muscle wasting. Their BMI may be slightly lower, but this does not necessarily mean they are underweight. In these instances, it is important to consult a dietitian who will provide helpful advice...